Barrel apparatus for barrel plating

ABSTRACT

A barrel apparatus for barrel plating in which a non-open type barrel is used, a workpiece is accommodated in the barrel and is immersed in a plating liquid, a negative electrode that is arranged within the barrel and a positive electrode that is arranged in the plating liquid are electrically connected and electroplating is performed while the barrel is rotated about a center shaft, includes a negative electrode arranged at a position that is in contact with a workpiece W inside the barrel, and a positive electrode is arranged at a position that is not in contact with the workpiece inside the barrel, wherein the barrel has a form that is substantially a cylinder or substantially a polygonal cylinder and a ratio between the diameter and the length thereof is in a range of 1:0.7 to 1:1.

TECHNICAL FIELD

The invention relates to a barrel apparatus for barrel plating in which a non-open barrel is used, a workpiece is accommodated inside the barrel and immersed in a plating liquid, a negative electrode that is arranged inside the barrel and a positive electrode that is arranged in the plating liquid are electrically connected and electroplating is performed while the barrel is rotated about a center shaft, and is specifically effective as measures for the environmental protection.

BACKGROUND ART

In a plating apparatus for industry, constant voltage control in which power supply is supplied to a plurality of barrels from one rectifier is performed. FIG. 5 shows a typical example of the above-described type of power supply. If the workpiece that is input into each barrel is different, the input amount is calculated beforehand and input so that a surface area of the workpiece is the same for each barrel. However, as shown in FIG. 5, if the lengths of the wires from the rectifier to each barrel are different from each other, electric current is easily flowed in order from the nearest rectifier so that the condition is not strictly the same as that for all the barrels.

Plating is based on Faraday's law and the amount of material that is deposited according to the electrolysis of electrolytic solution is proportional to an amount of electricity that is passed. The amount of electricity that is required to deposit material equivalent to 1 gram is constant despite the kind of the materials. In zinc plating, if 1.0 A of the electric current flows to a unit of an area of 1 dm² (10 cm×10 cm=100 cm²) for 1 hour, plating film 17.1 μm thick is deposited. The depositing speed is 0.285 μm/min, however in barrel plating, the plating film is deposited through the electric conduction by connecting an electricity conductor body (lead wiring) referred to as a conductor that is arranged inside a rotating barrel and a workpiece, so that there are many elements to hinder the calculation and there are many cases to depend on the skill of a worker.

In order to decrease the energy that is required to deposit the plating film, it is necessary to clarify the elements that are affected by the amount of electricity. The total amount of electricity that is used to deposit the plating film is decreased so that amount of CO₂ discharged is capable of being decreased. Here, lists of the elements that relate to decreasing the amount of CO₂ discharged and decreasing the running costs are described below.

-   -   Concentration of zinc metal inside the barrel is lowered in         accordance with the lapse of time.     -   The number of rotations of the barrel affects the deposited         amount (the film thickness) of the plating film that is formed         on the workpiece surface.     -   Volume of the barrel and a surface area of the workpiece that is         input affect the deposited amount (the film thickness) of the         plating film.     -   Concentration of zinc metal inside the plating tank needs to be         controlled to remain constant.     -   Liquid temperature inside the plating tank affects the deposited         amount (the film thickness) of the plating film.     -   Volume of the workpiece that is input affects the deposited         amount (the film thickness) of the plating film.     -   The surface area of an anode (a positive electrode) affects the         electric resistance.     -   The shape of the contact point related to electrical connection         at a time of electrically connecting to the internal electrode         affects the electric resistance.     -   The amount of electricity that is required to the deposit the         plating film (the film thickness) affects the setting of         electric current density.     -   The shape of the barrel hole affects the amount of chemicals         drawn out.     -   The amount of chemicals drawn out affects amount of the water         supply     -   The amount of chemicals drawn out affects the sludge in the         water discharging process.     -   The amount of the water supply affects the water discharging         process.

The inventor of the invention has reviewed barrel plating with respect to the above-described perspectives and a certain outcome is obtained with respect to the open type barrel and an application is filed with respect to a portion thereof. However, the open type barrel has an opening section at an end surface of the barrel in the direction of the rotation shaft and the workpiece is accommodated in a portion that is defined by the diameter of the opening and an inner diameter of the barrel so that this is not appropriate because there is a problem that for example, long bolt or the like may be highly possible to run over from the opening. Traveling type barrels can be distinguished in carrier type (see FIG. 5) or elevator type (see FIG. 6). Regarding the carrier type each of the processes is performed while a traveling vehicle (the carrier) moves the barrel. The elevator type is a type in which a process that is arranged endlessly with a pre-process tank and plating tank at a constant pitch, repeats that the barrel is rising-traveling horizontally-lowering-depositing per each pitch, in a constant time, and each of the processes is processed. In the carrier type, the diameter D of the barrel is small and the length L in the longitudinal direction is large (see FIGS. 7A and 7B). In a case where the workpiece that has a small volume is plated using above-described elongated barrel, the workpieces tend to easily separate from each other in the longitudinal direction and a problem may occur in the electrical connection so that the plating cannot be performed. These problems are more remarkable with small screws to be plated such as M2 to M4 size. If these screws are input in the barrel, their volume is about 151 (hereinafter, 1 is liter) per 50 kg of the inputting amount. Meanwhile, regarding large screws such as M16, the volume is about 601 per 100 kg of the inputting amount or 301 per 50 kg of the inputting amount. Thus, the volume of the large screws is two times of the small screws so that the above-described problems are difficult to issue. Also, example of the elongated barrel is a usual type in the carrier type barrel as disclosed in JP-A-2008-95143.

In the invention, according to the above-described knowledge, the barrel is non-open type and the knowledge that the length L thereof must be short rather than long is confirmed so that it is presupposed that the barrel apparatus is the elevator type. In the elevator type, the barrel is arranged so that the direction of the rotation shaft corresponds to the traveling direction of the barrel and the endless moving type that circulates a constant peripheral passage is taken. As a result, the length of the barrel is restricted to a constant pitch (distance between adjacent barrels) and this restriction means that the diameter D is large and the length L in the shaft direction is small regarding the barrel shape (FIGS. 8A and 8B), so that the case is appropriate in the invention. In order to establish a stable contact between the negative electrode and the workpiece inside the barrel, a minimum volume of the workpiece is required to be input and for this, the length L of the barrel is short and diameter D thereof is long, so that the condition of the inputting amount of the workpiece is also alleviated.

[Patent Document] JP-A-2008-95143

DISCLOSURE OF THE INVENTION Problem that the Invention is to Solve

The invention is made in view of the above points, and an object is to provide a plating apparatus for a barrel plating in which the non-open barrel is used so that even a long bolt class is capable of being plated without problem, furthermore electric resistance is decreased in the barrel plating from a small workpiece to a large workpiece and the discharging amount of CO₂ is capable of being decreased. Also, another object of the invention is to provide a plating apparatus for a barrel plating in which the barrel plating may be performed also using the plating apparatus of the related art that does not need to be basically changed. Also, decreasing of discharging amount of CO₂ and decreasing of running cost are capable of being obtained.

Means for Solving the Problem

To achieve above objects, the invention provides a barrel apparatus for barrel plating in which a non-open barrel is used. In the barrel plating process, a workpiece is accommodated in the barrel and immersed in plating liquid, a negative electrode that is arranged inside the barrel and a positive electrode that is arranged under plating liquid are electrically connected and electroplating is performed while the barrel is rotated about a center shaft. The barrel apparatus includes: a negative electrode arranged at a position that is in contact to the workpiece accommodated inside the barrel; and a positive electrode arranged at a position that is not in contact with the workpiece accommodated inside the barrel, wherein the barrel has a form that is substantially a cylindrical shape or substantially a polygonal cylindrical shape and a ratio of a diameter and a length thereof is in a range of 1:0.7 to 1:1.

As described above, according to the invention it is presupposed that the barrel apparatus is an elevator type barrel apparatus. As shown in FIG. 6, the plating apparatus of the elevator type takes an endless moving type that circulates along a constant peripheral passage and repeats the steps of pre-processing and plating during each cycle of rising→traveling horizontally→lowering→depositing (traveling horizontally or rising). Accordingly, all barrels are processed under the same conditions as the plating conditions, comprising the concentration of plating liquid and the electrical condition, may be considered as the same. As shown in FIG. 9, in a non-open barrel 10 that is used in the invention, both end surfaces (end portions) thereof are closed in the direction of the center shaft (axis) of the barrel and an opening portion is provided at the peripheral side surface of a rotation body. A lid C is provided at the opening section. The workpiece is accommodated inside the barrel and immersed in plating liquid. A negative electrode that is arranged inside the barrel and a positive electrode that is arranged within the plating liquid are electrically connected. The barrel plating that is performed while the barrel 10 is rotated about the center shaft is the object of the invention.

The apparatus of the invention includes a negative electrode 11 arranged inside the barrel 10 at a position that is in contact with the workpiece W accommodated inside the barrel and a positive electrode 12 arranged at a position that is not contacted to the workpiece W accommodated inside the barrel 10. FIG. 8 schematically shows a relation between the negative electrode 11 and the positive electrode 12 inside the barrel 10, and the workpiece W. In this case, the barrel 10 is adapted to be rotated such that the rotation thereof is counterclockwise with respect to the center shaft 13. In other words, the invention comprises an embodiment in which the positive electrode 12 is arranged at a position of the upper left portion of the barrel 10 that is apart from and opposite to the workpiece W that is deposited at the lower right portion inside the barrel 10 when the barrel 10 is rotated to the left (i.e. in the counterclockwise direction).

The barrel has substantially a cylindrical shape or substantially a polygonal cylindrical shape and a ratio of the diameter and the length of the cylinder is in a range of 1:0.7 to 1:1. FIG. 9 schematically shows the ratio between the diameter D and the length L of the barrel 10. In the ratio between the diameter D and the length L, By setting the lower limit of the length to 0.7 in the ratio of the diameter D and the length L the risk of relatively increasing the diameter of the barrel is avoided. The risk is that the auxiliary positive electrode is easily contacted to the workpiece and in a case of contacting, short may be occurred so that the rectifier may be damaged. Accordingly, in the invention, if a pitch is 900 mm, for example, a preferable example of the barrel is described in which the length is 580 mm, the diameter is 650 mm and the ratio is 1:0.89. However, if the inputting amount of the workpiece is increased or a workpiece having a long length is input, a design is chosen to increase the diameter of the barrel inside the range of the ratio between the diameter and the length. Also, as to the diameter of the barrel, if the material is PVC (vinyl chloride resin) or pp (polypropylene), the limit is about 800 mm. Thus, it is desirable that the ratio is 1:0.7.

Also, the positive electrode inside the barrel may constitute an auxiliary positive electrode. In this case, a main positive electrode may be arranged inside a plating tank where plating liquid is filled (and outside of the barrel) so that the positive electrode is along substantially periphery of the barrel. In the related art, where the electrical connection is established only by a main positive electrode that is arranged at the outside of the barrel, the barrel main body hinders the electrical connection so that the voltage tends to be increased. In the invention, a space inside the barrel is widened in the diameter direction and the auxiliary positive electrode is capable of being arranged inside the barrel that is widened space so that an advantage can be anticipated in which the voltage is lowered. The barrel main body has a plurality of barrel holes at the peripheral side surface thereof. In the invention, the barrel hole preferably has a long hole shape so as to allow easy inflow and outflow of the chemicals. According to a preferred configuration, the direction of the long hole is inclined with respect to the rotation direction thereof. In other words, the long holes have an orientation which is differt from the rotation direction of the barrel.

Advantage of the Invention

The invention has the above-described configuration and function in which a non-open barrel is used so that, when the ratio of the diameter and the length is in the range of 1:0.7 to 1:1 even the long bolt class is capable of being plated without problems. A further advantage is that the electric resistance is capable of being decreased in the plating of a small workpieces and of large workpieces. Also, according to the invention, the barrel apparatus for barrel plating may be provided, in which the discharging amount of CO₂ is capable of being decreased. Also, decreasing of discharging amount of CO₂ and decreasing of running cost are capable of being obtained, although the plating apparatus of the related art need not to be basically changed.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. FIG. 1 is a front view illustrating a barrel apparatus for barrel plating of an embodiment according to the invention. In each of drawings, 15 is a supporting column of the barrel plating apparatus, 16 is an elevator. The elevator 16 is provided capable of being elevated using the supporting column 15 as a guide rail and arranged to travel in an elevator type line in a direction parallel to the paper surface in FIGS. 1. 17 and 18 are hanger arms that are configured of a pair of members in right and left, and attached to the elevator 16 at a base end section. Bearing sections 19 and 21 for a rotation shaft of the barrel are provided at the front end section thereof respectively. A barrel main body 20 of the barrel apparatus according to the invention is attached to portions of the bearing sections 19 and 21 of both front and rear end sections in a suspension-supporting state.

In the embodiment shown in FIGS. 1 to 3, the barrel main body 20 has substantially polygonal cylinder shape configuration, the diameter thereof is 650 mm and the length thereof is 650 mm. Accordingly, a ratio between the diameter and the length of the barrel 20 is 1:1 so that it will be understood that the ratio is in a range of 1:0.7 to 1:1. The barrel main body 20 shown in drawings has the polygonal cylinder shape configuration having a nonagon cross-sectional shape and both end surfaces in the direction of the center shaft of the barrel are closed by end plates 22 and 23, and one end plate 23 also serves as a large gear. A plurality of holes is opened at the polygon peripheral side surface of the rotation body of the barrel main body and an opening section 24 is provided as an entrance of a workpiece W. An opening section 24 is provided openable by a lid 25. The shape of the barrel hole affects a drawing-out amount of chemicals so that it is desirable that the hole have a long hole shape (not shown) and the direction of the long hole be inclined with respect to the rotation direction of the barrel to facilitate inflow and outflow of the chemicals. The diameter of the barrel is relatively large so that the distance is long in the radial direction at the time of inflow and outflow of the chemicals. Accordingly, the barrel hole is the long hole and inclined with respect to the rotation direction so that inflow and outflow of the chemicals are capable of being smoothly performed.

The barrel apparatus of the invention includes a pair of right and left negative electrodes 26 and 26 that are arranged inside the barrel main body 20 and at a position to allow contact to the workpiece W. An inside positive electrode 27 that is arranged at a position that does not contact the workpiece W inside of the barrel 10 (the inside positive electrode 27 corresponds an auxiliary positive electrode in one embodiment). The negative electrodes 26 and 26 inside the barrel are attached to the barrel main body 20 at the position of the bearing sections 19 and 21. Also, the inside positive electrode 27 is arranged at a position of the upper right portion that is away from the workpiece W inside the barrel and opposite to the workpiece W that is deposited at the lower left portion inside the barrel main body 20 when the barrel rotates to the right in the embodiment shown in FIG. 1. In this case, it is assumed that the rotation of the barrel main body 20 is clockwise with respect to the center shaft. Also, 26 a represents a negative electrode lead wire (see FIGS. 1 and 3).

The inside positive electrode 27 has a laterally long rectangular shape and the longitudinal direction thereof is directed to be parallel with the center shaft direction of the barrel main body 20. A plate surface thereof is arranged inclined toward the workpiece in order to face to the workpiece that is in the left with respect to the rotation direction without contact the workpiece, at the time of inputting and at the time of rotation. Accordingly, a bracket 28 is screwed to the front and rear bearing sections 19 and 21 at both ends inside the barrel main body, and the inside positive electrode 27 is attached to the bracket 28 (see FIGS. 2 and 3). The bracket 28 also serves as a portion of a conductive member. Lead members 29 and 31 for the inside positive electrodes are fastened together by bolts that screw both ends thereof. Thus, the attachment of the members and the conductive passage are capable of being secured. A wiring from the conductive passage (not shown) is connected to the lead members 29 and 31.

A driving mechanism 30 is provided to rotate the barrel main body 20. The driving mechanism 30 has a motor 32 that is arranged at the base section of the hanger arm, a middle shaft 36 that is coupled to the motor 32 by pinions 33 and 34 and a chain 35, and reduction gears 37 and 38 that are at the other end of the middle shaft 36. The driving mechanism 30 drives a large gear 23 a that is provided at the outer periphery of the end plate 23 and a reduction gear 38. Also, the other end 26 b of the negative electrode lead wire 26 a communicates to a sliding mechanism 39 and can receive the power supply while moving.

In the barrel apparatus shown in drawings, the inside positive electrode configures the auxiliary positive electrode and a main positive electrode 41 is configured and arranged so as to be along the entire periphery of the barrel inside the plating tank 40 in which plating liquid is filled. The main positive electrode 41 includes a portion 41 a that is arranged to surround the workpiece W that is deposited to the left side of the barrel and a portion 41 b that is arranged at the outside of the inside positive electrode 27. The portion 41 a is provided to be easily and electrically connected to the workpiece W that is deposited to the left by the rotation of the barrel and the portion 41 b is provided so as to increase the area of the positive electrode. Especially, three positive electrodes 27, 41 a and 41 b are arranged to surround the periphery of the workpiece W that is deposited to the left. Accordingly, an advantage in which the electric current is easily flowed is obtained. 42 a and 42 b in the drawing are lead members for the positive electrode and connected to a wiring from the conductive passage (not shown). 43 is a base table of the plating tank.

<Plating Test>

Using the barrel plating apparatus configured as described above, the plating test is performed by the zinc plating and contents and results are described below.

<The Contents of Plating Test>

Test process: acid cleaning (using 35% of concentration of hydrochloric acid, during 15 minutes in a room temperature)→alkali electrolyte (using a electrolyte agent that is generally used for the zinc plating, during 5 minutes in room temperature)→temporary rust prevention (using 1% of concentration of caustic soda, during 1 minute in room temperature)→plating (according to a condition shown in Table 1 below)→post processing (using chromating agent, pH 2.4, during 30 seconds at 25° C.).

The workpiece that is used in the plating is M4×12 tapping screw, an inputting amount in barrel is 40 kg, a surface area is 25.0 dm²/kg, total surface area is 1000 dm², the plating liquid is Zn 13 g/l, NaOH 130 g/l, NaCO₃ 30 g/l, and as other luster, M3 agent 2 ml/l, B agent 0.3 ml/l are used.

TABLE 1 (Plating Condition) Electric current density (A/dm²)  1  0.5 Electric current and plating time 1000 A, during 10 minutes  500 A, during 68 minutes Voltage (V) 12.0 to 16.0 (1000 A)  8.0 to 12.0 (500 A) Barrel rotation (rotation/min.)  2 Temperature (° C.) 30 Barrel shape Octagon, barrel hole 16 × 3 mm

<Results of Plating Test>

TABLE 2 (Difference of Film Thickness by Presence or Absence of Auxiliary Positive Electrode) Auxiliary positive Auxiliary positive electrode is present electrode is not present Average film 8.34 7.17 thickness (μm) Maximum 9.62 7.85 Minimum 7.20 6.56

According to Table 2, 8.34 μm of average film thickness in a case where auxiliary positive electrode is present is increased in 11.6% with respect to 7.17 μm of average film thickness in a case where auxiliary positive electrode is not present and it is understood that large advantage is obtained. The result of the test is shown in a graph of FIG. 4. Peak of the film thickness in a case where auxiliary positive electrode is present is about 8 μm, meanwhile peak of the film thickness in a case where auxiliary positive electrode is not present is inferior to 7 μm. This shows that the difference and numerical values in Table 2 are meaningful.

In barrel apparatus for the barrel plating of the invention, as described above, the plating is capable of being performed with the plating time to be decreased so that the amount of electricity is capable of being decreased. As a result, the discharging amount of CO₂ is capable of being decreased.

In the embodiment, the barrel apparatus for the barrel plating of the invention is described applying to the zinc plating. However, the zinc plating is taken as a typical example thoroughly and the invention is not limited to the zinc plating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view illustrating an example of a barrel apparatus for barrel plating according to the invention.

FIG. 2 is an explanation side view illustrating the same apparatus.

FIG. 3 is an explanation plan view illustrating a main portion of the same apparatus.

FIG. 4 is a graph illustrating advantage according to the invention.

FIG. 5 is an explanation view illustrating a typical example of a power supply type of the related art.

FIG. 6 is an explanation view illustrating a plating apparatus of an elevator type where the invention is applied.

FIG. 7 is views illustrating a non-open barrel of the related art, A is a side view and B is a front view.

FIG. 8 is views schematically explaining the non-open barrel of the invention, A is a side view and B is a front view.

FIG. 9 is views illustrating an example of the same non-open barrel according to the invention, A is a side view and B is a front view.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   -   10 barrel schematically shown     -   11 negative electrode     -   12 positive electrode     -   13 center shaft     -   15 supporting column     -   16 elevator     -   17, 18 hanger arm     -   19, 21 bearing section     -   20 barrel main body     -   22, 23 end plate     -   24 opening section     -   25 lid     -   26 negative electrode     -   27 inside positive electrode     -   28 bracket     -   29, 31 lead member     -   30 driving mechanism     -   32 motor     -   33, 34 pinion     -   35 chain     -   36 middle shaft     -   37, 38 reduction gear     -   39 large gear     -   40 plating tank     -   41 main positive electrode 

1. A barrel apparatus for barrel plating in which a non-open barrel is used, a workpiece is accommodated in the barrel and immersed in a plating liquid, a negative electrode that is arranged inside the barrel and a positive electrode that is arranged in the plating liquid are electrically connected and electroplating is performed while the barrel is rotated about a center shaft, the apparatus comprising: a negative electrode arranged at a position that capable of being in contact with the workpiece accommodated inside the barrel; and a positive electrode arranged at a position that is not in contact with the workpiece accommodated inside the barrel, wherein the barrel has a form that is substantially a cylinder or substantially a polygonal cylinder and a ratio of a diameter and a length thereof is in a range of 1:0.7 to 1:1.
 2. The barrel apparatus for barrel plating according to claim 1, wherein the positive electrode comprises an auxiliary positive electrode arranged inside the barrel at a position that is not in contact with the workpiece and/or a main positive electrode arranged outside the barrel inside a plating tank where plating liquid is filled so that the main positive electrode is substantially along the periphery of the barrel.
 3. The barrel apparatus for barrel plating according to claim 1, wherein the barrel main body has a plurality of barrel holes at the peripheral side surface, the barrel hole has long hole shape so as to facilitate inflow and outflow of chemicals, and the direction of the long holes is inclined with respect to the rotation direction. 